Printing, copying or duplicating machines, such as rotary offset lithographic duplicating machines, normally are provided with some form of sheet receiving means at the exit end of the machine for stacking copy sheets issuing from the machine. Conventionally, the sheet receiving means include a receiving tray for receiving and stacking the sheets as the sheets fall by gravity and come to rest onto the top of a stack in the tray.
Many such machines employ conveyor means for delivering the sheets seriatim in a path outwardly over the receiving tray. Conventionally, the conveyor means includes a rigid gripper bar extending transversely between a pair of generally parallel, endless drive chains. Such conveyor means commonly are called chain delivery devices. The gripper bar has gripper fingers which grasp the sheets issuing, from the machine and direct the sheets outwardly over the receiving tray whereat the gripper fingers are timed for release of the sheets at very high speeds. Upon release, the sheets have a tendency, due to momentum to continue in their path of directed travel. Stripper devices, usually including stripper fingers which are transversely spaced so that the gripper fingers can pass therebetween, are used for engaging the lead ends of the sheets as the sheets issue from the conveyor means, "stripping" the sheets from the conveyor means, and directing the sheets downwardly into the receiving tray.
In some instances, the machine has some form of proofing mechanism at the exit end of the machine near the receiving tray. These mechanisms are provided whereby one or more sheets can be diverted or taken out of the normal stacking procedure in order to proof the copy for quality or apparent problems. For instance, it has been known to position an interrupter plate into the stack of sheets for pulling a sheet out of the stack for proofing purposes and so that continuous delivery of the sheets onto the stack is not interrupted.
Proofing copy sheets becomes a considerable problem in machines which have finishing stations, particular where the sheets are sequentially numbered. A very common example is serially numbered bank checks or drafts. Of course, there are many other instances where it is desirable to number the copy sheets as they exit from the printing couple of the machine.
It can be understood that if a numbered copy sheet is removed from the normal delivery system, that numbered sheet must somehow get back into the stack in its proper place or order. This can be very time consuming and, with heavy stock paper or large size copy sheets, very cumbersome. Further, placing the proofed copy back into the stack most often disorients the stack and causes problems with further processing of the copy sheets.
This invention is directed to a novel system for proofing copy sheets exiting from a printing or duplicating machine, particularly in applications where the machine includes a sheet numbering system.